This invention relates to broadband integrated circuit double-balanced mixers suitable for use in the microwave and millimeter wave bands and capable of broad intermediate frequency (IF) bandwidths, extending to microwave frequencies.
As microwave systems progress into the millimeter wave spectrum, it becomes necessary to develop broadband components for applications in this frequency range. Much of this development involves band extensions of lower frequency systems to 60 GHz and higher. For example, broadband receivers for the 18 to 42 GHz range might split the band into six 4 GHz wide channels, each of which is down converted to a common microwave IF band, say 2 to 6 GHz or 4 to 8 GHz, using a separate mixer. The IF output is then processed further by an existing microwave system.
The invention is directed to the provision of broadband mixers suitable for such millimeter wave down-converter applications. Typical system requirements on such down-converters call for low noise, high IF output frequencies, minimal spurious response, and low cost. Small size and weight are frequently desired. To minimize system noise figure, mixers should have low conversion loss and have a balanced mixer configuration. IF bandwidths should extend at least to 8 GHz. To minimize intermodulation spurious responses, they should be fundamentally rather than subharmonically pumped, and have a double-balanced configuration. Low cost potential, and small size and weight call for the use of microwave integrated circuit technology. Broad RF bandwidths are also desirable, even in cases where the required bandwidth may be no greater than the individual millimeter channel width, so that one mixer can cover many channels without individual tuning.